This invention relates to telecine machines or converters for scanning film to produce a television signal, which is of the type using a linear light sensor, such as a solid state line array.
Such telecine machines have been referred to in British Pat. Nos. 1,479,976 and 1,526,801, and use the motion of the film to provide the vertical component of the scanning, and the scanning circuits in the sensor to provide the horizontal scanning. Thus the telecine machine comprises a linear light sensor array, a light source, drive means for moving film at a constant rate between the light source and the sensor array in a direction substantially perpendicular to a plane containing the sensor array, optical means for imaging an illuminated section of film on the sensor array, and electronic means for deriving a television signal from the sensor array and for converting it from sequential to interlace form.
This system is used to produce broadcast television signals, which need to be of one of the standard formats, such as 625/50 (625 lines per picture and 50 interlaced fields per second) or 525/60 (525 lines per picture and 60 interlaced fields per second). Other standards using 405 and 819 lines exist but are of decreasing importance.
Difficulties arise in the scanning film on two accounts. The first is that the ratio of the number of active lines of the television picture to the total number of lines per picture interval may not be the same as the ratio of the height of each film frame to the interframe pitch on the film. For convenience I shall refer to these two ratios as the utilization ratio of the television picture and of the film respectively.
The second problem is that the picture rate of the television signal in pictures per second may not be the same as the film speed in film frames per second.
Proposals have been made for overcoming these difficulties. For instance, to compensate for differences in utilization ratios, it has been suggested that the television signal could be processed to increase the number of the scanned lines which contain the active picture. Such an operation is complex and involves a large amount of storage as well as fairly sophisticated interpolation.
I have appreciated that the problem can be overcome much more simply.